There is usually (always?) a hidden disk partition that is reserved for the OS. It is well hidden and tools like diskpart are needed to see that it even exists. Presumably that is your problem.
The default size for the reserved partition has seemingly increased over the years so if this device is older and has not clean installed Windows in a long time it might be almost full.
All that said I have no idea if there is a way to prune this partition to make space.
There is usually (always?) a hidden disk partition that is reserved for the OS. It is well hidden and tools like diskpart are needed to see that it even exists. Presumably that is your problem.
The default size for the reserved partition has seemingly increased over the years so if this device is older and has not clean installed Windows in a long time it might be almost full.
All that said I have no idea if there is a way to prune this partition to make space.